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An almost totally inconclusive meta-analysis of studies of Vitamin D for pain

PainSci » bibliography » Wu et al 2016
Tags: treatment, pain, vitamin D, nutrition, self-treatment

One article on PainSci cites Wu 2016: Vitamin D for Pain

PainSci commentary on Wu 2016: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

There are good reasons (including some evidence, e.g. see Schreuder) to hope that vitamin D supplementation is valuable for some kinds of pain patients, but it remains speculative. This is the first “major” meta-analysis of trials, but arguably it’s premature: just not enough data to meta-analyze meaningfully. Although 19 studies and 3,436 participants might seem like plenty, that includes studies of a wide variety of conditions — too wide, everything from fibromyalgia to osteoarthritis to migraine. It would be surprising if any treatment had a consistent effect on such different problems! This isn’t just a “limitation” of the meta-analysis, it’s a sucking chest wound. Although the authors did compare results in two meaningful categories (regional pain versus widespread pain), there were still too many different kinds of conditions within those categories. (Diabetic neuropathy definitely does not work the same way as rheumatoid arthritis.)

Despite this major flaw, Vitamin D still seemed to work on average, at least a little bit. They detected a small improvement, about a half point (on a 10-point pain scale). Would you bother taking a pain-killer for a 5% improvement? Probably not: that is a classic example of a clinically trivial benefit, the bare minimum required for better-than-nothing, but still right at the edge of giving-a-crap, and of detectability. But it probably worked better for some patients, and not at all for others.

Also completely missing from this study is any hint of whether more is better. Or whether D2 or D3 is better. Or whether a longer course of supplementation is better. Or whether any improvement was related to blood serum D levels.

The main thing this study tells us is that the evidence is far too limited and still can’t really tell us the value of vitamin D for any specific kind of pain patient.

This is the same conclusion reached by Straube et al in 2016.

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND: There is conflicting evidence from previous qualitative reviews on the effect of vitamin D supplementation on pain.

OBJECTIVE: To determine with quantitative methods if vitamin D supplementation lowers pain levels.

STUDY DESIGN: Quantitative meta-analysis of published randomized controlled trials (RCTs).

SETTING: This meta-analysis examined all studies involving the effect of vitamin D supplementation on pain score.

METHOD: Electronic sources (Medline, Embase, Cochrane Central Register of Controlled Trials, clinical trials website, and Google scholar) were systematically searched for RCTs of vitamin D supplementation and pain from inception of each database to October 2015.

RESULTS: Nineteen RCTs with 3,436 participants (1,780 on vitamin D supplementation and 1,656 on placebo) were included in the meta-analysis. For the primary outcome (mean change in pain score from baseline to final follow-up), 8 trials with 1,222 participants on vitamin D and 1,235 on placebo reported a significantly greater mean decrease in pain score for the vitamin D group compared to placebo (mean difference -0.57, 95% CI: -1.00 to -0.15, P = 0.007). The effect from vitamin D was greater in patients recruited with pre-existing pain (P-value for interaction = 0.03). Fourteen studies (1,548 on vitamin D, 1,430 on placebo) reported the mean pain score at final follow-up outcome, and no statistical difference was observed (mean difference -0.06, 95%CI: -0.44 to 0.33, P = 0.78). In 4 studies which reported pain improvement (209 on vitamin D, 146 on placebo), the effect size although not significant, shows participants in the vitamin D supplementation group were more likely to report pain improvement compared with the placebo group (relative risk 1.38, 95%CI: 0.93 to 2.05, P = 0.11).

LIMITATIONS: Only a few studies reported the mean score change from baseline to final follow-up, and we do not have enough data to determine any modifying effect of baseline vitamin D status and different doses of vitamin D supplementation on pain.

CONCLUSION: A significantly greater mean decrease in pain score (primary outcome) was observed with vitamin D supplementation compared with placebo in people with chronic pain. These results suggest that vitamin D supplementation could have a role in the management of chronic pain.

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